Prosopis tree named ‘Sonoran’

ABSTRACT

A new and distinct combination of the genes of South American Prosopis alba and North American Prosopis glandulosa var glandulosa for cold hardiness and erect growth to produce erect, thornless, fast growing ornamental and lumber trees that provide greater adaptability to a much broader range of arid ecosystems than previous Prosopis alba ornamental selections.

Latin name of the genus and species of the plant claimed: P. alba x P. glandulosa var glandulosa hybrid.

Variety denomination: ‘Sonoran’.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application has a copending application Ser. No. 16/501,518 cultivar ‘Mojave’ which is a full sibling of previously patented clones as described below.

BACKGROUND OF THE INVENTION Field of the Invention

As exemplified by extensive native distribution on the floor of Death Valley, Calif. that is the hottest place on earth, the nitrogen fixing genus Prosopis has exceptional heat drought tolerance. Prosopis lumber has very low shrinkage and almost equal radial and tangential shrinkage leading to widespread use for fine furniture, flooring and architectural components in southwestern United states, Mexico and Argentina. Its exceptional heat/drought tolerance and broad canopy have led to widespread use as an ornamental tree, particularly in arid California and Arizona. Lack of tolerance to extended periods of 10° F. have limited the use of the most widespread ornamental species with lack of thorns i.e. P. alba in southwestern USA. The presence of thorns on cold hardy native species P. glandulosa and P. velutina and their lack of erect growth have limited its use for ornamentals. Water shortages and water rationing for landscaping in southwestern USA make ornamental trees with low water requirements especially desirable.

In Argentina more than 100,000 tons of logs per year were harvested in the early 2000's for flooring and furniture manufacture but this industry has greatly decreased due to overharvest of native trees. In Texas Prosopis lumber harvested from non-cultivated trees is the basis for a substantial cottage industry. Lack of thornless native Prosopis with erect growth, and lack of hardiness to approximate 5° F. temperatures of the thornless south America P. alba has resulted in lack of plantations necessary to be a commercial lumber tree in the USA. I have used classical breeding techniques to obtain the best combinations of cold hardiness, erect growth and lack of spines from elite North and South American Prosopis species.

Specifically, I have crossed a previously described cold hardy spineless Prosopis alba with a cold hardy spineless and very erect Prosopis glandulosa var glandulosa and selected progeny that are spineless, cold hardy, fast growing and very erect for use both as ornamentals and lumber producing trees.

Description of Relevant Prior Art

In this patent, the species descriptions of Burkart (1976). A monograph of genus Prosopis (Leguminosae). Journal of Arnold Arboretum; 450-525. has been followed. The parents of the claimed plant described here are the U.S. Plant Pat. No. 9,256 thornless Prosopis glandulosa var. glandulosa ‘Beth’ that has exceptionally erect growth with narrow branch angles and the U.S. Plant Pat. No. 9,072 thornless P. alba ‘Laurie’ that survived 20 consecutive hours below 20° F. with a minimum of 10° F.

Other patented Prosopis clones for use as ornamentals are ‘American Mesquite’ (U.S. Plant Pat. No. 24,702) that resulted from a seedling of unknown parents, with unknown cold tolerance at this Arizona nursery, ‘Leslie Roy’(U.S. Plant Pat. No. 23,360) that originated from a cross between an unnamed P. velutina and an unnamed P. chilensis and is stated to be cold hardy to USDA Zone 7b as it withstood a temperature of minus 12° C. (10° F.) and ‘Cooper’(U.S. Plant Pat. No. 15,303) that was stated to be P. alba, but according to Burkart (1976), due to its leaflet spacing was a P. chilensis. In Argentina where the author lived for 5 years, temperatures briefly reach minus 12° F. but little damage results to the P. alba due to the less than a one hour early morning duration of the freeze. In contrast the ‘Laurie’ P. alba parent survived 20 consecutive hours below 20° F. with a minimum of 10° F. and 10 years without damage in Austin, Tex. which is USDA cold hardiness zone 8B.

In 2011 hand crosses were made between ‘Laurie’ and ‘Beth’ in a greenhouse in Salinas, Calif. using the ‘Laurie’ as the pollen donor and the ‘Beth’ as the female parent. The seeds were planted in the same greenhouse on Dec. 4, 2011. On June 2014, progeny of these crosses were first successfully asexually propagated by wedge grafting with greater than 80 success. After the cloned progeny were evaluated for erect and spineless habit over a 5 year period in a greenhouse in Salinas Calif., and field plantings at a research facility in Vista, Calif., the ‘Sonoran’ and the copending ‘Mojave’ application were discovered and selected for patenting.

The foliage pattern and branch angle has remained constant through more than 2000 wedge grafts through succeeding asexual propagation over an 8-year period onto P. alba x P. glandulosa rootstock as well as P. alba rootstock in a greenhouse in Salinas, Calif. and in Vista, Calif.

While ‘Sonoran’ and ‘Mojave’ were not tested for freeze hardiness, as the most frost susceptible parent, the P. alba ‘Laurie’ is cold hardy to USDA zone 8B and the ‘Beth’ Texas native parent P. glandulosa var glandulosa is cold hardy to all of Texas (USDA zones 7A and 6b) it is reasonable to assume that the progeny will possess cold hardiness similar to the most susceptible parent i.e. zone 8B.

SUMMARY OF THE INVENTION

For the first time the ornamental tree characteristics of an elite clone of the North American species i.e. thomlessness, cold hardiness to 0° F. and a special erect habit, have been combined with characteristics of an elite the South American Prosopis i.e. fast growth, thomlessness and more tropical looking foliage (more pinnae and more closely spaced leaflets) to provide a better suite of characteristics than either of the parents, or other Prosopis clones being used for ornamentals.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 of a 2.5-year-old clone ‘Sonoran’ in the greenhouse in a 10 gallon container illustrates the very rapid growth and non-drooping form of this clone.

FIG. 2 (in mm) illustrates the variation in the bi-pinnate leaf form.

FIG. 3 in mm illustrates the variation in pod shape size and color.

FIG. 4 illustrates the color and morphology of the flowers and

FIG. 5 illustrates the trunk characteristics.

DETAILED BOTANICAL DESCRIPTION OF THE PLANT

All color designations herein are made in accordance with The Royal Horticultural Society Colour Chart Third Edition. This plant ‘Sonoran’ is one of the progeny of hand crosses between Prosopis alba (native to Argentina) variety ‘Laurie’ as the pollen parent and Prosopis glandulosa var glandulosa (native to south Texas) ‘Beth’ as the female parent, and thus is an interspecific hybrid. Unlike the P. alba parent with 4 pair of pinnae and with 52 pairs of leaflets per pinnae or the P. glandulosa parent with one pair of pinnae with 10 leaflets per pinnae, ‘Sonoran’ has 2 pairs of pinnae with about 30 pairs of leaflets per pinnae, each about 2.6 mm wide, 12 mm long and with a 2.2 mm spacing between leaflets on the pinnae. The venation of the leaflets is not distinguishable. The 12 cm pinnae length of this new clone was similar to both the P. alba parent with 11-13 cm length or the P. glandulosa parent with a pinnae length of 12-13 cm.

The color of the leaves is Green Group 140C. Upon first frost, the mature leaves fall off and no color change is seen. Nectaries are not visible.

The pods shown in FIG. 3 (in mm) are intermediate in color and form between the patented P. glandulosa var glandulosa parent (FIG. 4 of ‘Beth’) and the P. alba parent (sheet 2 of 4 of U.S. Plant Pat. No. 09,072). The pods of ‘Sonoran’ are 14.6+/−0.78 mm wide and were similar to width the P. alba parent of 14-16 mm but are wider than the P. glandulosa parent i.e 9 mm. The pods with a thickness 5.1+/−0.47 mm were similar to both the P. glandulosa var glandulosa parent with 5 mm thickness and the P. alba parent with 4-6 mm thickness. The ‘Sonoran’ pods had a mean length of 12.8+/−1.77 cm which is shorter than the 17-20 cm for the P. glandulosa parent but similar to the 8-11 cm length for the P. alba parent. Some of the ‘Sonoran’ pods were slightly curved unlike the perfectly straight P. glandulosa parent but less curved than the P. alba parent. ‘Sonoran’ pods had reddish streaks (greyed-purple group 187 A) similar to the P. glandulosa parent and completely different than the yellow tan pods (with no reddish coloration) of the P. alba parent.

The number of pods per inflorescence can range from zero to 10 depending on the pollination. Since Prosopis is 100% self-incompatible, if no other Prosopis is close, or no bees are present, no pods will be produced. Similarly, if many trees of the same ‘Sonoran’ clone are used in large plantings, no pods will result. No pod production from extensive plantings could be desirable in an urban landscape project where the pods must be removed but not desirable where abundant wildlife is the objective.

The seeds per pod is variable with more seeds the longer the pod. The seeds have a greyed-orange 165 A color are oval shaped and are approximately 5.5 mm wide and 8.2 mm long.

The branching angle, sometimes also known as the “crotch angle” is very important in lumber trees as well as ornamental trees. The P. alba parent had a weeping, pendulant branching habit with no central stem above 2 m and had several co-dominant main branches with crotch angles of about 60-80 degrees i.e. only slightly above horizontal. In contrast the angle subtended by the main branches from the central trunk in the very unique P. glandulosa clone was about 20-25 degrees and therefore was much more vertical than the P. alba parent.

Flowering habits: The range in color and shape of several inflorescences that each contain several hundred perfect, self-incompatible flowers with 10 stamens are shown in FIG. 4. The inflorescence is approximately 5 cm long and 1.5 cm in diameter. The immature inflorescence to the far left is green group 142A. Several solitary flowers that remained on the rachis, each with 10 stamens, of color yellow 12A can be seen in the center and a very mature inflorescence in which the withers have senesced of color yellow group 5A, is shown on the far right. The flowers do not have an odor. Flowers are minute and too small for accurate measurements.

Distinguishing characteristics of copending applications of full siblings: As can be seen in the table below, ‘Sonoran’ can be distinguished from ‘Mojave’ of the copending application by the presence of small spines and by average distance between leaflets on the pinnae. In addition, the girth of ‘Sonoran’ is about 4 mm less than ‘Mojave’ for a 2-meter-tall tree of the same height.

TABLE 1 Comparison between ‘Mojave’ and ‘Sonoran’ Aver- age of Dis- Aver- tance Aver- Aver- Aver- Aver- age # be- age age age age of of tween of # of of Spine leaflet leaflets leaf- pairs pinnae Leaflet len- length per lets of length width gth Clone (mm) pinnae (mm) pinnae (mm) (mm) (mm) ‘Mojave’ 11.1 30.8 1.6 2.0 11.0 2.4 0.0 ‘Sonoran’ 12.4 30.2 2.2 2.0 11.6 2.6 5.0

General tree characteristics. Depending on management, the annual diameter growth ranges from about ½ to ¾ inch per year and the height growth from 3 to 6 ft per year. A 10-year-old tree under good management will be about 6-8 inches in diameter at breast height and 20-25 ft tall. The color of the trunk is Greyed-Red group 177 b with Greyed-Red Group 163A colored lenticels. Except for the tropical P. pallida which is not deciduous, all other species are deciduous, and while ‘Sonoran’ is deciduous it loses its leaves approximately a month after P. glandulosa. The tree has a salinity tolerance to at least 8 dS/m. The clone has a high temperature tolerance of 115° F. and low temperature tolerance of USDA cold hardiness zone 8b. ‘Sonoran’ is resistant to the fungal pathogens Lasiodiplodia, Pestialopsis and Phymatotrichum omnivorum. In addition, the girth of ‘Mojave’ is about 4 mm greater than ‘Sonoran’ for a 2-meter-tall tree of the same height. 

The invention claimed is:
 1. A new and distinct variety of Prosopis tree named ‘Sonoran’ for use as ornamentals and lumber that combines the unique characteristics of North and South American Prosopis species including cold hardiness to USDA zone 8b, thornlessness, erect growth with branch angles less than 20 degrees, and fast growth as described and illustrated herein. 